Paint Quantity Calculator Guide: How Much Paint Do You Need?
Quick Answer
- *One gallon of paint covers 350–400 sq ft on smooth walls — that's roughly one coat for a 12 × 12 room.
- *Always plan for two coats when changing colors, covering repairs, or using dark/vivid shades.
- *Textured surfaces like stucco reduce coverage to 200–300 sq ft per gallon.
- *Buy 10–15% extra for touch-ups — running out mid-project is the most common painting mistake.
The Basic Paint Coverage Formula
The formula is straightforward: Total wall area ÷ Coverage rate per gallon × Number of coats = Gallons needed.
For a rectangular room, calculate wall area as: (2 × length + 2 × width) × ceiling height. Then subtract openings: a standard door is about 21 sq ft, and a standard window is about 15 sq ft.
Coverage Rates by Paint Type
| Paint Type | Coverage (sq ft/gallon) | Best For |
|---|---|---|
| Interior Latex (flat/matte) | 350–400 | Bedrooms, ceilings, low-traffic areas |
| Interior Latex (eggshell/satin) | 350–400 | Living rooms, hallways, kitchens |
| Interior Latex (semi-gloss) | 350–400 | Bathrooms, trim, doors |
| Exterior Latex | 250–350 | Siding, fascia, outdoor surfaces |
| Primer | 300–350 | New drywall, stain blocking, color changes |
| Stain (deck/fence) | 150–300 | Varies widely by wood porosity |
These rates assume smooth, previously painted surfaces. According to Behr's 2024 paint coverage study, porous or textured surfaces consume 25–50% more paint than smooth drywall.
Room-by-Room Paint Estimates
These estimates assume 8-foot ceilings, standard door and window deductions, and two coats of interior latex paint:
| Room Size | Wall Area (approx.) | Gallons Needed (2 coats) |
|---|---|---|
| 10 × 10 ft (small bedroom) | 280 sq ft | 1.5–2 |
| 12 × 12 ft (standard bedroom) | 334 sq ft | 2 |
| 14 × 16 ft (living room) | 420 sq ft | 2.5 |
| 20 × 20 ft (large room) | 560 sq ft | 3–3.5 |
| Bathroom (5 × 8 ft) | 160 sq ft | 1 |
According to HomeAdvisor's 2025 Home Improvement Report, the average American homeowner paints 2.3 rooms per painting project and spends between $200 and $500 on paint alone (including primer).
When You Need One Coat vs Two Coats
One Coat May Suffice When:
- Repainting the same color or a very similar shade
- The existing surface is in good condition with no patches
- Using a premium paint-and-primer-in-one product
Two Coats Are Recommended When:
- Changing from dark to light (or light to dark)
- Covering patched or repaired areas
- Painting new drywall, even if primed
- Using vivid or deep colors (reds, yellows, deep blues)
- Painting over wallpaper removal areas
Benjamin Moore's technical data sheets show that even their best paints achieve only 92–96% opacity in one coat over a contrasting surface. The second coat brings that to 99%+ and ensures uniform sheen.
How Surface Texture Affects Coverage
Texture is the biggest variable in paint quantity estimation. Rough surfaces have more surface area per square foot and absorb more paint into pores and crevices.
| Surface Type | Coverage Adjustment | Approx. sq ft/gallon |
|---|---|---|
| Smooth drywall | Standard | 350–400 |
| Orange peel texture | –10% | 315–360 |
| Knockdown texture | –15% | 300–340 |
| Popcorn ceiling | –25% | 260–300 |
| Stucco (exterior) | –30 to –40% | 210–280 |
| Brick | –40 to –50% | 175–240 |
According to PPG Industries, painting brick requires up to 2× the paint volume compared to smooth drywall for the same square footage. Always do a test section on highly porous materials.
Calculating Paint for Trim, Doors, and Ceilings
Trim and Baseboards
One quart of trim paint covers approximately 75–100 linear feet of standard baseboard (3.5–5.5 inches tall). For a 12 × 12 room, that's about 48 linear feet — well under one quart. Most homeowners need 2–3 quarts total for a whole-home trim project.
Doors
A standard interior door has about 21 sq ft of paintable surface (both sides). One quart covers 2–3 doors with two coats. Panel doors use slightly more paint than flat doors due to recessed areas.
Ceilings
Ceiling paint is typically flat/matte and covers the same 350–400 sq ft per gallon. For a 12 × 12 room, one gallon handles the ceiling with one coat. Popcorn or textured ceilings need 25–30% more. According to a 2024 Sherwin-Williams contractor survey, only 35% of DIY painterspaint the ceiling when they repaint a room — but pros recommend it for the best visual result.
Paint Cost Estimation
Paint prices vary significantly by quality tier. Here are typical 2025 retail prices per gallon:
| Quality Tier | Price per Gallon | Examples |
|---|---|---|
| Budget | $25–$35 | Glidden, Valspar (basic line) |
| Mid-range | $40–$55 | Behr Premium Plus, SW ProClassic |
| Premium | $55–$80 | Benjamin Moore Regal, SW Emerald |
| Ultra-premium | $80–$100+ | Benjamin Moore Aura, Farrow & Ball |
Consumer Reports' 2024 paint rankings found that mid-range paints ($40–$55) offered the best value for DIY painters, scoring within 5% of premium paints on coverage and durability tests while costing 30–40% less.
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Frequently Asked Questions
How much does one gallon of paint cover?
One gallon of interior latex paint covers approximately 350–400 square feet on smooth, primed surfaces with one coat. Textured surfaces like stucco or brick can reduce coverage to 200–300 square feet per gallon. Exterior paint covers slightly less — typically 250–350 square feet per gallon due to rougher surfaces and higher porosity.
How many gallons of paint do I need for a 12×12 room?
A 12 × 12 room with 8-foot ceilings has approximately 384 square feet of wall area. Subtract about 50 square feet for a standard door and two windows, leaving 334 square feet. At 350–400 sq ft per gallon, you need 1 gallon for one coat. For two coats (recommended when changing colors), buy 2 gallons. Add a quart for the ceiling if painting it separately.
Do I need one coat or two coats of paint?
Two coats are recommended in most situations: when changing colors, painting over patches or repairs, using dark or vivid colors, or painting new drywall (even if primed). One coat may suffice if you are repainting the same color or a very similar shade and the existing surface is in good condition. Premium one-coat paints offer better coverage but cost 40–60% more per gallon.
How do I calculate paint for trim and baseboards?
Measure the total linear feet of trim and multiply by the trim height (typically 3.5–5.5 inches for baseboards, 2.5–3.5 inches for crown molding). One quart of trim paint covers about 75–100 linear feet of standard baseboard. For a typical 1,500 sq ft home, plan on 2–3 quarts of trim paint for baseboards and door casings combined.
Should I buy a little extra paint?
Yes. Buy 10–15% more than your calculated amount. You will need extra for touch-ups after furniture placement, picture hanging, and normal wear. Sealed paint lasts 5–10 years when stored properly (cool, dry place, 50–80°F). According to Sherwin-Williams, the number one customer complaint is running out of paint mid-project.